Composite electron microscope grid suitable for energy dispersive X-ray analysis, process for producing the same and other micro-components

ABSTRACT

A composite electron microscope grid for support of specimens and suitable for energy dispersive X-ray analysis is fabricated from a low atomic number composite material comprising a polymer formed from a combination of some or all of carbon, hydrogen, oxygen and nitrogen, to which carbon, preferably in the form of carbon fibers is blended. The dispersed carbon in the polymer strengthens the grid and greatly increases the electrical and thermal conductivity of the resultant grid so as to minimize the otherwise present electron charge buildup in the vicinity of the grid during the electron bombardment associated with the X-ray analysis. The high thermal conductivity of the grid minimizes the temperature rise in the grid and specimen under analysis; thereby ensuring a stable specimen image. 
     The composite grids according to the present invention are fabricated from an etched surfaced mold which is sacrificed after the grid casting. Preferably, the mold is made from a material with a different solubility or chemical resistance than the composite material forming the grid so that the mold can simply be dissolved after use. The mold itself is preferably etched using a photoresistive process for precisely etching the desired grid structure into the mold material. The mold process for making the grid can be utilized for molding other types of micro-components.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electron microscope grids and a processfor making the same and also to general applications of the disclosedmolding process for fabricating other types of micro-components.

2. Description of the Prior Art

The present invention describes a process of producing very small partshaving extremely precise tolerances by a micro-molding process in whichthe mold is sacrificed after the casting of the part is completed. Thismicro-molding process is particularly suited for manufacturing specimensupports, such as grids for use in electron microscopy having typicaldiameters of 3.0 millimeters, typical thicknesses of 1.5 mils (38.1microns) and line widths of about 150 microns.

In the last decade, electron microscopy has placed increasing emphasison the use of the electron microscope as an analytical tool to determinethe composition and structure of a specimen rather than simply as adevice capable of producing a highly magnified image. One analyticalmethod of increasing importance is energy dispersive X-ray analysis.Here, the X-rays emitted from the specimen when bombarded by an electronbeam activates a solid state detector and, after being analyzed in amulti-channel analyzer, are displayed in a spectrum where each spectrumpeak can be used to identify the presence of a particular element in thespecimen.

This procedure is complicated by two factors. First, the electrons arescattered by the specimen and by the interior of the microscope columnitself. The electrons can strike the specimen support, generally a finemesh screen or grid 3 millimeters in diameter as explained earlier, andscatter in various directions. In addition, electrons can strikeapertures or any part of the column above the sample producing highenergy X-rays which can also strike the grid and be scattered therefrom.Both of these processes cause the grid to produce large amounts of X-rayradiation which produces noise in the spectrum of the multi-channelanalyzer.

Since the typical specimen placed on the grid has a thickness of onlyabout 1,000 angstroms while the thickness of the grid itself isapproximately 1.5 mils (approximately 380,000 angstroms), the grid isfar more massive than the specimen and consequently produces a signalwhich can in some cases completely mask the detection of trace elementsin the specimen. This noise generated by the support has in the pastbeen complicated by impurities within the grid material, especiallyimpurities having high atomic numbers. That is, the noise generated bythe support is dependent not only upon the size of the support but alsoupon the atomic numbers of the various constituent elements forming thematerial comprising the support. Indeed, the contribution in the energyspectrum due to the grid material is not necessarily limited tofrequency peaks at specific frequencies in the spectrum but can alsopresent a "continuum radiation" spread over the entire energy spectrum.The higher the elemental atomic numbers of the material forming thegrid, the greater the severity of the continuum radiation interference.

Currently, in electron microscopy, specimen support grids are often madefrom copper. These grids are inexpensive and readily manufactured viaelectrolytic deposition or chemical etching. They are generally found tobe adequate when only the imaging capabilities are of interest. However,due to the noise factors mentioned earlier, difficulty arises in the useof copper in energy dispersive X-ray analysis. Its high atomic number,29, results in the generation of noise over a considerable range of theenergy spectrum. Thus, since copper is not one of the carbon, hydrogen,oxygen and nitrogen primal elements of organic matter, its use as aspecimen support can completely mask the presence of trace elements inthe specimen which might easily be detected if the specimen support wasalso fabricated from a material formed from carbon, hydrogen, oxygen andnitrogen.

Attempts at solving this problem have in the past generally involved theuse of grids made from elements with as low an atomic number aspossible. Thus, beryllium, a metal with atomic number 4, has been usedin fabricating grids. However, beryllium is toxic and is extremelydifficult to produce in highly purified form. Consequently, grids madefrom this material have been quite expensive, costing about five dollarsper grid.

Grids made from woven nylon, a material comprising carbon, hydrogen,oxygen and nitrogen, are also commercially available. While the signalto noise ratio in the X-ray spectrum is improved with nylon grids andwhile such grids are non-toxic, such grids present problems even moresevere than beryllium. First such grids are non-conducting and thuscause a problem when bombarded with an electron beam; namely, thegeneration of electron charge build-up in the vicinity of the grid andspecimen which seriously degrades the image quality of the dispersiveX-ray analysis equipment. In addition, since the nylon grids whenfabricated are stamped out from a woven nylon mesh, they are non-rigidwith freedom of deformation in both Cartesian axes of the grid plane.Since the electron beam heats the grid during the X-ray analysis of thespecimen, the grid's resultant thermal expansion causes it to deform orcreep, thereby preventing a stable specimen image from being observed.Finally, most commercial plastics contain halogen compounds as well astrace amounts of high atomic number elements which are added during theformation of the plastic for purposes of acting as catalysts, hardeners,flame retardants and other similar purposes. All of these additionaltrace elements further interfere with the energy-dispersive X-rayanalysis of the specimen which is generally attempting to discover thepresence of trace elements in the specimen.

One proposed solution to the specimen support problem is a grid formedprimarily from carbon. Since carbon is a low atomic number element(atomic number 6), is non-toxic and a conductor of heat and electricity,it was believed that making grids from such a material would meet allthe structural, heat and electrical conductive requirements of a gridwhile exhibiting low amounts of X-ray spectral noise. Attempts were madeto produce a grid entirely of carbon by sputtering several layers ofcarbon atop of each other and, in some cases successive pyrolyzing ofthe deposited carbon. However, it was discovered that grids produced inthis fashion were extremely delicate and unable to withstand themechanical stresses encountered in the normal course of handling duringspecimen preparation.

The present invention is believed to overcome these deficiencies inprior art specimen support grids for energy dispersive X-ray analysis bybeing fabricated from a composite material comprising polymers includingengineering plastics formed from a combination of some of all of thefollowing organic primal constituent elements--carbon, hydrogen, oxygenand nitrogen--in dispersive mixture with carbon in the range of 10% to90% by weight.

The composite material is thus formed from the same low atomic numberelements ordinarily found in the organic specimens and therefore isnon-toxic while generating minimal interfering spectrum noise. Theblending of the carbon into the polymer greatly increasing theelectrical and thermal conductivity of the composite material therebyminimizing electron charge buildup and thermal expansion of the supportand specimen. The blended carbon, especially when in the form of fibers,also adds structural strength to the resultant support.

The process by which these grids are fabricated; namely, the formationof the desired mold by photochemical etching, the casting of the gridsfollowed by dissolving the mold with a substance that does notchemically attack the grids, provides a method by which other extremelysmall micro-components, such as gears and escapements, can be moldedinexpensively without damage or distortion.

SUMMARY OF THE INVENTION

An electron microscope specimen support or grid is fabricated accordingto the present invention from a composite material comprising a polymerformed from a combination of some or all of the followingelements--carbon, hydrogen, oxygen and nitrogen--in blended dispersivecombination with powdered carbon or carbon fibers so as to yield a gridhaving advantageous properties for energy dispersive X-ray analysis;namely, minimal X-ray radiation noise, structural rigidity to giveadequate support to the specimen while preventing movement of thespecimen during its exposure to electron bombardment, heat conductivityto minimize the temperature buildup of the grid and the specimen thereonduring exposure to the electron bombardment, and high electricalconductivity to bleed off the otherwise present electron charge buildupin the vicinity of the grid and specimen due to electron bombardment.The composite grid is preferably fabricated by a micro-molding processin which the molding material is made from a material with a differentsolubility or chemical resistance than the specimen support composition.The mold is prepared by etching the desired grid pattern therein by anyof several well-known techniques including photo-resist techniques, orlaser or, electron-beam lithography.

When using the photo-resist technique, any residuals of the photo-resistis removed from the surface of the mold following the metal etching.Once the mold has been properly etched, it is ready for application ofthe desired composite material. In one version of this process, thecomposite material is a resin which is still in the liquid state atambient conditions to which a catalyst and carbon in various forms isblended. The liquid mixture is applied to the etched regions by simplypouring the liquid over the surface of the mold. Any excess compositemixture remaining on the surface of the mold is removed with a doctorblade or similar device.

In another embodiment of this process, the composite material comprisesthermosetting polymers to which carbon is blended. This compositematerial is applied to the etched regions of the mold by a compressionmolding machine. In this latter technique, the polymer and carbon blendare heated to a desired temperature to insure melting with sufficientpressure applied to insure that the composite material has filled theetched regions of the mold. The mold containing the composite materialis then allowed to cool until it has solidified.

Following application of the composite material into the mold, excessmaterial above the surface of the mold is removed by any of severaltechniques including sanding, grinding and milling. Following this step,the mold is sacrificed by dissolving it in a suitable solvent or bychemically converting the mold to a soluble compound by using a solventwhich is chemically inert with respect to the grid forming compositematerial. The destruction of the mold leaves the grid intact and readyto use.

This molding technique may be utilized in fabricating othermicro-components. Due to the destruction of the mold without attackingthe micro-components, the stresses to the components that would occurwhen using release agents and mechanical removal devices is eliminated.Micro-molding is therefore readily and inexpensively attained.

OBJECTS OF THE INVENTION

Therefore, it is a primary object of the present invention to provide acomposite electron microscope specimen support or grid suitable forenergy dispersive X-ray analysis fabricated from a composite materialhaving all constituent elements of low atomic number, the resulting gridhaving sufficient structural rigidity for support of a specimen,sufficient thermal conductivity to prevent excessive heating of thespecimen and grid and deformations thereto, as well as sufficientelectrical conductivity to remove generated electron charge about thespecimen and grid during the dispersive X-ray analysis;

An additional object of the present invention is to provide a specimensupport or grid or the above description further fabricated from acomposite material comprising a polymer composed of a combination ofsome or all of the following elements--carbon, hydrogen, oxygen andnitrogen--and carbon blended therewith in a concentration of 10% to 90%by weight;

An additional object of the above invention is to fabricate specimensupports of the above description to which a trace element or compoundhas been blended with the composite material in order to provide adesired analytic standard;

Another object of the present invention is to provide an electronmicroscope specimen support or grid of the above character which can bereadily and inexpensively manufactured in a process whereby a mold isfabricated from a material having a different solubility than thespecimen support forming material and which can be easily etched withthe desired micro-mold cavity and sacrificed after the casting has beencompleted;

A further object of the present invention is to provide a processcapable of not only making specimen supports of the above character butalso other micro-components by preparing a mold etched with cavitieshaving the shape of the desired components whereby the mold issacrificed by dissolving it in a solution which does not chemicallyattack the molded components;

A still further object of the present invention is to fabricate electronmicroscope specimen supports or grids of the above character wherein thepolymer is a fluid resin at ambient conditions to which the carbon andcatalyst is added so as to flow the composite material into the cavitiesof the mold with the material subsequently polymerizing prior tosacrifice of the mold;

Another object of the present invention is to provide a process of theabove character for making micro-components including electronmicroscope grids, in which the polymer is of a thermosetting variety towhich carbon fibers are blended, wherein the polymer composite isinserted into the cavities of the mold by compression molding techniqueswith subsequent curing of the polymer composite prior to sacrifice ofthe mold; and

Other objects of the present invention will in part be obvious and willin part appear hereinafter.

THE DRAWINGS

For a fuller understanding of the nature and objects of the presentinvention, reference should be had to the following detailed descriptiontaken in conjunction with the following drawings, in which:

FIG. 1 is a greatly enlarged top plan view of a composite electronmicroscope specimen support or grid fabricated according to the presentinvention, showing a specimen in phantom;

FIG. 2 is a greatly enlarged, cross-sectional partially cut away, sideelevational view of a portion of the grid shown in FIG. 1 illustratingits use to support a specimen, the specimen in phantom and its thicknessnot drawn to scale;

FIG. 3 is a greatly enlarged, partially cut away, top plan view of amold fabricated according to the present invention for use in makinggrids as shown in FIG. 1;

FIG. 4 is a greatly enlarged, cross-sectional, side elevational view ofa portion of the molding material illustrating the first step in theprocess of fabricating the mold by applying a photo-resist material tothe top of the mold material;

FIG. 5 is a top plan view of the mold shown in FIG. 4 showing the gridpattern masked onto the photo-resist prior to exposing and developingthe photo-resist;

FIG. 6 is a partially cutaway cross-sectional side-elevational view ofthe mold shown in FIG. 5 illustrating the dissolved portions of thephoto-resist material after exposing and developing thereof with asolvent that dissolves the formerly masked portions of the photo-resist;

FIG. 7 is a partially cutaway cross-sectional side-elevational viewsimilar to FIG. 6 and illustrating the etching of the mold materialbelow the dissolved portions of the photo-resist;

FIG. 8 is a cross-sectional partially cutaway side-elevational viewsimilar to FIG. 7 illustrating the mold after the photo-resist materialhas been removed and prior to the casting of the composite material toform the molded part;

FIG. 9 is a cross-sectional side-elevational view similar to FIG. 8illustrating one method of casting the composite material into theetched portions of the mold; namely, by forcing the composite materialtherein by a compression molding machine;

FIG. 10 is a cross-sectional side-elevational view similar to FIG. 8illustrating another method of casting the composite material into theetched portions of the mold; namely, the pouring the material when in aliquid state over the etched surface of the mold;

FIG. 11 is a cross-sectional partially cutaway side elevational viewsimilar to that shown in FIG. 9 illustrating the mold material castedinto the etched out cavities of the mold after the residual compositematerial has been removed from the surface of the mold;

FIG. 12 is a cross-sectional partially cutaway side elevational viewsimilar to that shown in FIG. 11 after the mold has been dissolvedillustrating the molded components in its final form;

FIG. 13 is an energy-dispersive X-ray spectrum produced by a prior artcopper specimen grid;

FIG. 14 is an energy-dispersive X-ray spectrum produced by a prior artberyllium specimen grid; and

FIG. 15 is a similar energy-dispersive X-ray spectrum as shown in FIGS.13 and 14 but illustrating the spectrum produced by a specimen gridfabricated according to the present invention.

DETAILED DESCRIPTION

As best shown in FIGS. 1 and 2, a composite electron microscope specimensupport or grid 15 according the present invention is typically a round,flat disc with a diameter of approximately 3.0 millimeters, a thicknessof 1.5 mils (38.1 microns) and line widths of 150 microns. Specimensupports include grids and also include planchet discs normally placedatop a metallic stud in energy-dispersive X-ray equipment. Such discshave in the past been generally fabricated from beryllium. The grids ofthe present invention are especially suited for energy dispersive X-rayanalysis in which they are used to support a specimen 16, typically ofan organic nature and having a thickness of approximately 1,000Angstroms (0.0001 millimeters). In energy dispersive X-ray analysis, thegrid 15 and specimen 16 are exposed to electron bombardment typicallyfrom an electron microscope, or other source of electrons, so that theX-rays emitted from the specimen produced by the bombardment of theelectron beam can activate a solid state detector. This detection of theelectron beam is then typically analyzed in a multi-channel analyzer anddisplayed in a number of counts v. energy spectrum of the type shown inFIGS. 13-15 so as to enable the scientist to identify the presence oftrace elements in the specimen.

However, this procedure is complicated by two factors. First, theelectrons are scattered by the specimen and by the interior of themicroscope column. These scattered electrons can then strike thespecimen grid support 15. Also, the electrons that strike apertures orany part of the microscope column above the specimen can produce highenergy X-rays which can also strike the grid. The electrons that scatterfrom the specimen to the grid as well as those high energy X-rays whichstrike the grid directly produce large amounts of X-ray radiation whichproduce noise in the frequency spectrum of the specimen being analyzed.The grid, which typically has a thickness of 1.5 mils (38.1 microns) ismuch more massive than the specimen 16, which typically has a thicknessof approximately 1,000 Angstroms, and therefore the signal produced fromthe grid material and its impurities can be sufficient to completelymask the detection of small amounts of trace elements in the specimen.In order to minimize the spectral noise of the grid, it is desirable tofabricate the grid from a pure material comprising only low atomicnumber elements.

A grid manufactured from plastic, such as pure nylon, would achieve thelow atomic number constituent element criterion necessary for minimizingspectrum noise. However, the known molding techniques prior to thepresent invention, have been unable to produce finished products usingsuch plastics. Thus, although nylon grids have been fabricated for useas specimen grids, these grids have been fabricated using weavingtechniques for making a mesh which is stamp cut to generate the grid.However, this form of grid is undesirable since it does not have aperipheral member and therefore is able to deform when subjected to heatbuildup from electron bombardment. Furthermore, woven nylon grids havenot been made with carbon blending of the nylon but have at most beencoated with carbon for obtaining electrical and thermal conduction. Suchcoatings have typically not eliminated the heat buildup and electroncharge buildup in the vicinity of the grid during electron bombardmentresulting in thermal expansion and consequent deformation of the gridduring X-ray analysis with a resultant unstable specimen image beingobserved. Furthermore, such organic grids, due to the manufacturingprocesses used in making the nylon, include trace amounts of high atomicnumber elements which are added for purposes of acting as catalysts,hardeners, flame retardants and similar functions. These trace elementsfurther interfere with the disperse X-ray analysis.

The specimen supports of the present invention can be fabricated fromany polymer having as its constituent elements combinations of some orall of carbon, hydrogen, oxygen and nitrogen. These polymers includepolycarbonates, acrylics, epoxies, polyesters, styrenes andpolyethylenes and all other suitable organic polymers of which the aboveare a suitable representation. The present process for fabricating thesegrids utilizes a molding technique which eliminates the structuralweaknesses in the nylon woven grids. The present grids also yieldrelatively low spectral noise since the composite material from whichthey are fabricated comprise a polymer and carbon with the same lowatomic number elements as the organic specimens normally undergoinganalysis. Since the energy-dispersive X-ray analysis is usually lookingfor trace elements other than the carbon, hydrogen, oxygen and nitrogenprimal elements of organic specimens, the spectrum interferencegenerated by a grid made from a composite polymer material consisting ofsuch elements is relatively innocuous. Furthermore, due to the moldingprocess of the present invention, carbon or other low atomic numberelectrical conductive material is intermixed with the polymer during themolding process so as to be equally dispersed throughout the polymer andthereby provide the electrical and heat conductivity desirable in X-raydispersive analysis specimen supports. As indicated earlier, theelectrical conductivity of the grid is able to bleed away the otherwisegenerated electron charge in and about the grid and specimen which addsfurther spectral noise to the system analyzing the specimen. Carbon inthe form of fibers, lamp black and graphite also provides good thermalconductivity for heat sinking the specimen to the other X-ray analysisequipment and thereby minimize the temperature increase of the specimenand grid during the electron bombardment. By minimizing the temperatureincrease of the grid and specimen, the tendency for the grid to deformdue to thermal expansion is greatly minimized enabling a high resolutionspecimen image to be achieved.

In addition, other additives may be blended into the polymer to yieldparticular desired peaks in the dispersive X-ray spectrum. Thus, thisinvention does not limit itself to the sole use of carbon as an additivein the composite material forming the specimen support, but includes allother elements which may be blended into the polymer individually or incombination, to yield desired properties or peaks of known magnitude foruse as analytic standards. These composite materials can readily bemolded into the desired forms of the specimen supports as set forthlater in this description.

THE PROCESS Mold Preparation

As best seen in FIG. 4, the first step in preparing the specimen grid isto coat a planar surfaced mold material 18 formed from a metal such ascopper, with a photo-resist 20. This photo-resist coating and moldmaterial is then baked. Following this operation, the desired shape ofthe grid is photographically imprinted onto the photo-resist 20utilizing standard photo-engraving techniques. Thus, as shown in FIG. 5,the regions 22 of the photo-resist which are to have the shape of thedesired grid are photographically masked with the remainder of thephoto-resist surface exposed to ultra-violet light. In the negativephoto-resist process preferably used in the present invention, themasked portions will dissolve away after the photo-resist is developedin a suitable solvent system. FIG. 5 illustrates the portions 23remaining after the photo-resist is developed.

After the photo-resist has been developed with the desired shape of thegrid, it is again baked to harden the remaining portions of thephoto-resist, especially the perimeter of dissolved portions 23. Theunprotected metal areas beneath the dissolved portions are then etchedby using a chemical solution such as a solution of nitric acid or ferricchloride. Such a solution etches metal 18 as shown in FIG. 7 but doesnot attack the photo-resist material 20. The metal can be etched to anydesired depth by periodically visually observing the degree of etchingwith a standard optical microscope. Once the desired etched depth hasbeen obtained in the metal, the metal may be flushed with water or otherinert solution with respect to the metal leaving the etched portions 24in the metal as shown in FIG. 7. For electron microscope grids, thedepth of the etched image in the metal is typically between 1.5 and 3.0mils (38.1 to 76.2 microns).

Once the proper depth has been obtained in the metal molding material,the etching is terminated and the photo-resist is removed by anappropriate stripper so as to generate the finished mold 26 in themolding material 18 as shown in FIG. 8. The mold is then complete andready for casting.

Micro-Component Fabrication

Once the mold 26 has been prepared according to the preceding process,it is ready for casting micro-components such as specimen support grids.The etched portions 24 of the mold 26 comprise a cavity 27 to be filledwith the desired material for forming the micro-component. For castingelectron microscope grids the mold, as shown in FIG. 2, incorporates aplurality of grid cavities 27 so as to form many grids at the same time.In general, the mold is etched with a plurality of micro-componentcavities in order to reduce the cost and time to fabricate eachmicro-component. For fabricating electron microscope grids, the castingmaterial can be any polymer consisting of a combination of some or allof carbon, hydrogen, oxygen and nitrogen along with desired additionalelements or compounds for achieving desired electrical and heatconductivity and other properties mentioned earlier.

Two methods may be employed for filling the mold cavity with thecomponent material 31. A first method is to spread a liquid over theetched portions of the mold. For making specimen support grids, a resinstill in the liquid state at ambient conditions to which a catalyst isadded is spread over the etched portions of the mold so as to flow intothe cavities and fill them with the composite liquid 31 as shown in FIG.10. Such resins which are in the liquid state at ambient conditionsinclude momomers requiring a catalyst for polymerization which aregenerally referred to as two component systems such as epoxies andpolyesters. These resins when mixed with a suitable catalyst will becomepolymerized and thus solidified in the etched portions of the mold 26.The excess resin across the surface 28 of the mold 26 can be removed byuse of a doctor blade or other suitable device prior to completepolymerization resulting in the etched portions of the mold being filledas shown in FIG. 11.

For making specimen support grids, carbon in the form of fibers, lampblack or graphite and known trace elements can be blended with the resinand catalyst prior to application onto the mold so as to yield thedesired electrical and heat conductive qualities for fabricatingelectron microscope grids and for producing analytic standards forenergy dispersive X-ray analysis.

Alternatively, as shown in FIG. 9, thermosetting polymers such asnylons, polycarbonates and polystyrene can be used as the componentmaterial to fill the etched portions 24 of the mold when fabricatingspecimen support grids. As shown in FIG. 9, a standard compressionmolding machine 30 is placed over the surface 28 of the mold forcing thethermosetting polymer into the etched portion 24 of the mold as well asabove the surface of the mold. The compression molding machine appliesthis material at a high pressure and an elevated temperature to insurethat the polymer 31 has filled all of the mold cavity. Followingapplication of the polymer, it is allowed to cool unitl it hassolidified at which time its shape is as shown in FIG. 10.

For making micro-components in general, materials in addition tothermosetting polymers can be forced into the mold cavities usingcompression molding machines. The excess material 31 above the surfaceof the mold can be removed by any of several machining methods includingsanding, grinding or milling. It is of couse desired to remove all ofthis excess material so that none of it remains on the surface of themold with only the etched portions of the mold 24 filled with material31 as shown in FIG. 11.

The machineing methods may also be used to remove the photo-resist if itis desired to by-pass the step of stripping the photo-resist followingetching of the mold as shown in FIG. 8.

Once the composite material has been inserted and solidified into thecavities of the mold as shown in FIG. 11, the cast components are thenready for separation from the mold. This separation of the castings fromthe mold is obtained by the different solubility or chemical resistanceof the molding material with respect to the casting material. Thus, themold is simply inserted into a suitable solvent or reagent whichdissolves the molding material but which does not attack the solidifiedcasting material 31. Thus, the mold is sacrificed leaving the discretecomponents intact and ready to use without further fabricationoperations. Alternatively, the mold may be chemically converted into asoluble compound for again sacrificing the mold, leaving the castingsintact. By sacrificing the mold, micro-size components such as electronmicroscope grids can be removed from the mold without employing therelease agents and mechanical moving devices currently used in mostmolding techniques.

For such micro-components, the use of release agents or mechanicalremoval means would impose such severe stress on the components thatthey would be either distorted or broken, and thereby rendered useless.

As would be obvious to one of ordinary skill in the art, the mold mayalso be sacrificed by fabricating it from a material with a lowermelting point than the component forming material and heating the moldto its melting point after component casting.

Examples of the described molding techniques to form micro-componentelectron microscope specimen support grids are set forth below:

EXAMPLE I

Electron microscope specimen support grids having a diameter of 3.0millimeters, a thickness of 1.5 mils (38.1 microns), and line widths of150 microns were prepared utilizing the described process with a fluidresin. The mold material was prepared from copper foil. A coating ofphoto-resist material known as KTFR, manufactured by the Eastman KodakCompany, Rochester, N.Y. was then applied and baked with the moldmaterial. The photofabrication techniques used were those as set forthin Photofabrication Methods With Kodak Photosensitive Resists, publishedby Eastman Kodak, which is hereby incorporated by reference. Thephoto-resist then was masked with the above grid patterns and properlyexposed with an ultraviolet photoflood light source for five minutes andat a distance of three feet. The photo-resist was then developed withKMER developer (also manufactured by Eastman Kodak) until the maskedareas of the photo-resist were dissolved down to the surface of the moldmaterial. A post bake then followed with the mold surface subsequentlyetched by a 25% solution of ferric chloride where the photo-resist wasdissolved. The etching of the metal was terminated at a depth of 1.5mils (38.1 microns).

The formulation of the material to be used in forming the casting (grid)consisted of 100 parts polyester resin, 1.5 parts peroxide catalyst, and100 parts carbon in the form of a graphite powder. This grid materialformulation was poured over the etched surface of the mold and allowedto cure for eight hours in order to reach the desired degree ofpolymerization. The excess polymer on the surface of the mold was thenremoved by sanding. The filled mold was then dissolved in a 25% solutionof nitric acid leaving the discrete casted grids as the end product.These grids were suitable for use as specimen supports in electronmicroscopes.

EXAMPLE II

In this example, the mold was prepared as described in Example I. Aftermold preparation, a polymer mixture consisting of 100 parts acrylicpowder and 100 parts carbon powder in the form of graphite waspreblended to insure homogeneous composition. The mixture was insertedinto the cavities of the mold by a compression molding unit wherein themold and mixture was pre-heated to 300° F. and subjected to 3,000 poundsper square inch pressure (2.07×10⁷ newtons per square meter) for fiveminutes and then allowed to cool. The excess polymer composite materialon the surface of the mold was removed by sanding and the filled moldwas then dissolved in a 25% solution of nitric acid leaving discretegrid components as described in Example I.

The present invention as disclosed herein describes electron microscopespecimen support structures fabricated from polymers consisting ofcombinations of some or all of the organic matter constituent elements(carbon, hydrogen, oxygen and nitrogen) to which carbon has been blendedso as to be suitable in energy dispersive X-ray analysis. The additionalblending of additives for analytical standards can also readily beobtained in the support structures formulated according to the presentinvention.

Furthermore, the present invention describes a process for fabricatingthe support grids having the chemical compositions previously describedby first fabricating a mold formed from a material having a differentsolubility than the material forming the grid. The mold is preferablyfabricated using photo-resist photo engraving techniques with the gridmaterial casted into the etched portions of the resultant mold with theexcess mold material removed from the surface of the mold. Followingthis operation, the mold is sacrificed preferably by insertion of themold into a solution which dissolves the mold material but to which thegrid material is chemically inert. The resultant grids are thereforeobtained without the necessity for any additional operations necessary.

The above described methods for fabricating the grids having thechemical formulation previously described can also be used in formingother micro-sized components, such as miniature gears, where standardmolding techniques utilizing release agents or mechanical removing meansare unsuitable due to the small size and delicate nature of the castedcomponents.

It will thus be seen that the objects set forth above, and those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in carrying out the above process,products resultant therefrom, and in the composition set forth for themolded components without departing from the scope of the invention, itis intended that all matter contained in the above description or shownin the accompanying drawings shall be interpreted as illustrative andnot in a limiting sense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

Having described the invention, what is claimed is:
 1. A specimensupport, for use with an electron microscope having an energy dispersiveX-ray device for receiving spectral X-rays produced from the electronbombardment of the specimen and the specimens support, said support(A)being responsive to electron bombardment to produce spectral X-ray peaksranging between the X-ray energy of hydrogen and the X-ray energy ofoxygen; (B) being electrically conductive; and (C) comprising acomposition essentially of a homogeneous blend of(a) between about 10%and 90% by weight of a hydrocarbon polymer, and (b) between about 10%and 90% by weight of elemental carbon,whereby the X-ray energy of thespecimen support produced by the electron bombardment never exceeds theX-ray energy of oxygen, thereby providing a specimen support thatsubstantially eliminates spectral X-ray peaks which could interfere withthe X-ray peaks of the specimen.
 2. An energy dispersive X-ray analysisspecimen support as defined in claim 1, wherein the support has theshape of a grid with a rim about its periphery.
 3. The specimen supportfor use in electron microscopy defined in claim 1, wherein said supportcomprises a grid.
 4. An electron mircoscopy grid as defined in claim 3wherein the carbon is in the form of graphite or fibers.
 5. An electronmicroscopy grid as defined in claim 4 wherein the grid compositionfurther comprises trace amounts of an additive blended with the carboninto the polymer so as to yield desired spectral peaks in energydispersive X-ray analysis for use as an analytic standard.
 6. Anelectron microscopy grid as defined in claim 4 wherein the polymer isselected from the group consisting of polycarbonates, acrylics,polyesters, styrenes, and polyethylenes.
 7. An electron microscopy gridas defined in claim 4 wherein the grid is round with a peripheral rimthereabout for facilitating structural rigidity.
 8. The specimen supportfor use in energy dispersive X-ray analysis defined in claim 1, whereinthe composition is further defined as comprising a hydrocarbon polymerincorporating one selected from the group consisting of oxygen andnitrogen.
 9. A specimen support as defined in claim 1 wherein the carbonis in the form of graphite or fibers.
 10. A specimen support as definedin claim 9 wherein the composition further comprises trace amounts of anadditive, responsive to electron bombardment to produce a known, definedspectral X-ray energy, said additive being blended with the carbon intothe polymer to yield the known spectral X-ray peak in the energydispersive X-ray analysis, thereby providing an analytic standard forcomparitive analysis at any desired position along the output spectrum.11. A specimen support as defined in claim 9 wherein the polymer isselected from the group consisting of polycarbonates, acrylics,polyesters, styrenes, and polyethylenes.
 12. A specimen support asdefined in claim 9 wherein the support is a round grid with a peripheralrim thereabout for facilitating structural rigidity.
 13. The energydispersive X-ray analysis specimen support defined in claim 1, whereinthe support comprises a plurality of intersecting specimen supportingarms forming a latticed structure, defining a plurality of open zonessubstantially uniformly distributed throughout the support, with each ofsaid open zones comprising a mesh size between about 50 and 400 mesh, asdefined by the Tyler screen scale.
 14. The specimen support defined inclaim 13, wherein said support further comprises a rim peripherallysurrounding the supporting arms and contacting the terminating endsthereof.
 15. The specimen support defined in claim 14, wherein said rimcomprises a substantially circular shape, and said plurality ofintersecting support arms are substantially perpendicularly disposed toeach other, forming a latticed structure comprising substantiallyrectangularly shaped openings.
 16. The specimen support defined in claim9 wherein the graphite is further defined as comprising graphite powder,and the carbon fibers are further defined as being randomly oriented anddistributed throughout the support.
 17. The specimen support defined inclaim 1, wherein said support comprises a planchet.
 18. The specimensupport defined in claim 17, wherein the planchet is further defined ascomprising a substantially circular shape with a diameter of betweenabout one-half inch (1.25 cm) and one inch (2.5 cm) and a thickness ofbetween about 1/8 inch (0.15 cm) and 1/8 inch (0.3 cm).
 19. The specimensupport defined in claim 1, wherein the hydrocarbon polymer is furtherdefined as incorporating one selected from the group consisting ofnitrogen and oxygen.